1. Field of the Invention
The present invention relates to an optical path monitoring device and an optical path monitoring system which monitors the state of an optical path such as an optical fiber.
Priority is claimed on Japanese Patent Application No. 2008-165761, filed Jun. 25, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
As is generally known, an optical time domain reflectometer (OTDR) is a device which identifies optical transmission characteristics and abnormal points of an optical path by detecting a back scattered light of an optical pulse irradiated as a measuring light to the optical path. The optical time domain reflectometer is used as a measuring device or a monitoring device for an optical path.
An optical path monitoring system, which is a combination of an optical time domain reflectometer, an optical power meter (OPM) and a personal computer, has recently become commercially practical. The optical path monitoring system controls the optical time domain reflectometer and the optical power meter by using the personal computer, and is applied to an optical path for optical communication. That is, in the optical path monitoring system, under control of the personal computer, the optical power meter detects levels of optical communication signals received from an optical path, and in the case where the optical signal level is abnormal, the optical time domain reflectometer identifies abnormal points of the optical path.
For example, Japanese Unexamined Patent Application, First Publication No. 2008-020229 discloses the details of the above optical path monitoring device.
However, in the above conventional optical path monitoring system, after the personal computer determines that an optical communication signal level is abnormal based on the detection result of the optical power meter, the computer supplies a measuring start instructions to the optical time domain reflectometer, so that the optical time domain reflectometer identifies abnormal points of the optical fiber. In this case, the dead time is defined between from when the personal computer determines that the level of the optical communication signal is abnormal to when the optical time domain reflectometer starts measurement. The conventional optical path monitoring system cannot identify an abnormal point of a short time abnormal phenomenon in the optical fiber. The short time abnormal phenomenon may be a phenomenon such that the optical path is instantaneously interrupted. The short time abnormal phenomenon occurs only within a short period of time, for example, about 1 s. The above-described dead time is a short period of time. In some cases, the short time abnormal phenomenon occurs only within the dead time. In this case, the conventional optical path monitoring system is hardly performed to identify the abnormal point.
Furthermore, the optical time domain reflectometer obtains measuring signals by averaging waveforms of back scattered lights relating to a plurality of optical pulses by signal processing, and then locates and visualizes abnormal points based on the measuring signals. Consequently, the time of measurement performed by the reflectometer becomes relatively long so that it hinders from identifying abnormal points relating to the above short time abnormal phenomenon. Therefore, the conventional optical path monitoring system cannot identify abnormal points relating to a short time abnormal phenomenon and thus it is not practically useful.